A DNA-BASED INVESTIGATION OF INTESTINAL MICROBIOTA OF INFANTS AND THE IMPACT OF PREBIOTICS AND MATERNAL INTESTINAL MICROBIOTA

by Williams, Timberly Ann

Abstract (Summary)

Human milk provides ideal nourishment for infants. Human milk promotes an intestinal microbiota predominated by beneficial bacteria such as bifidobacteria and lactobacilli, and human-milk oligosaccharides are thought to be among the major factors responsible for such a prebiotic effect. Supplementation of infant formulas with various prebiotics (indigestible oligosaccharides) has been tested to close the gaps of the intestinal microbiota between human milk-fed and formula-fed infants. However, conflicting conclusions have been drawn. The overall objective of this research is to investigate the intestinal microbiota of term infants as impacted by feeding (human milk vs. infant formula), supplementation of oligosaccharides, and maternal intestinal microbiota. An integrated cultivation-based and DNA-based molecular biology approach was used to both quantify the abundance of the microbiota and to assess its bacterial diversity. In the first clinical study, supplementation of fructo-oligosaccharide (FOS) to an infant formula was tested for its prebiotic effects. Despite considerable variations among the infants of each feeding group, the formula supported a comparable abundance of bifidobacteria and lactobacilli as human milk but a higher population of E. coli and Clostridium difficile, and the FOS supplementation did not significantly affect the abundance of these bacteria. In order to investigate the prebiotic effects without the host-associated confounding factors, a second study was conducted in-vitr. Of the prebiotics tested, at doses tolerated by infants, galacto-oligosaccharides (GOS, at 7.2 g/L) had the greatest prebiotic effects: increased bifidobacterial growth and acetate production, and decreased culture pH and E. coli population, followed by oligofructose-enriched inulin (at 4 g/L). Inulin (at 0.8 g/L), either alone or when added to GOS, did not produce any of the significant prebiotic effects. Based on denaturing gradient gel electrophoresis (DGGE) profiling, the third study was designed to access the impact of maternal intestinal microbiota on both human milk-fed and formula-fed infants. The bifidobacterial diversity significantly exceeded that of lactobacilli and Bacteroides irrespective of feeding. Based on co-occurrence of sequenced DGGE bands, the maternal intestinal microbiota appeared to influence that of her infant in a species- and mother-infant, pair-dependent manner. A greater maternal impact was observed on the intestinal lactobacilli and Bacteroides among the human milk-fed infants than formula-fed infants.